Vertical cavity lasers with monolithically integrated refractive microlenses

摘要

Refractive microlenses (34, 38) are monolithically integrated into back-emitting vertical cavity lasers. A back-emitting VCL (20, 36) includes a front mirror, a back mirror being partially transmissive, an optical cavity interposed between the front mirror (22) and the back mirror (24), an active region within the optical cavity (26, 40) between the front and back mirrors, and a substrate (30). The substrate (30, 44) confronts the back mirror (24) and presents a light-emitting back surface (32). A refractive microlens (34, 38) is formed on the back surface (32) of the substrate (30, 44) with a photoresistive polymer or is monolithically integrated into the back surface (32) of the substrate (30, 44) using the photoresistive polymer. In microlens processing, poly(dimethylgluterimide) (PMGI), a deep ultraviolet photoresist is spin-coated on the polished back surface (32) of the substrate (30, 44) containing the fabricated VCL (20, 36). An imaging layer of conventional positive photoresist is spin-coated and patterned on the VCL. The PMGI is exposed to deep ultraviolet light using the patterned positive photoresist as a portable conformal mask. The exposed PMGI is then developed away and the positive photoresist is removed using acetone. The resultant structure is a cylinder of PMGI. A thin layer of the substrate around the PMGI cylinder is recessed. The PMGI cylinder is reflowed at 300 DEG C for 5-15 minutes. A parabolic lens shape of reflowed PMGI is obtained and is transferred to the substrate (30, 44) using reactive ion etching.